A test for comparing the means of two samples, or the mean of one sample (or even parameter estimates) with a specified value; also known as the "Student t-test" after the pseudonym of its inventor.

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11 views

F-Test for Equality of Variances with Weighted Survey Data

I would like to use an F-Test for Equality of Variances on a variable to compare two groups. Normally, this would be done with an sdtest command in Stata or a ...
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2answers
34 views

ttest or wilcoxon

for a user study I want to compare some tasks. Each tasks has 2 conditions on a intervall scale. From each task I want to test the the conditions with: a t-test if both samples are on a normal ...
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1answer
20 views

How do I statistically test whether two intervention types have significantly different effects in a meta-analysis?

I have the following problem: I am researching the difference in effects (as measured by standarized mean differences (SMD)) of two intervention types. (let's call them intervention 1 and intervention ...
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1answer
360 views

95% confidence intervals and the null hypothesis

I have performed an unpaired t-test comparing the means of two groups. My hypothesis was that the stroke group mean would be significantly higher than the control group mean. However, the t-test ...
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2answers
224 views

Statistically significant?

I am new to statistics and so any help would be greatly appreciated! I have done a study looking at the number of samples being sent to the lab for patients with UTIs in a GP practice. I then ...
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0answers
17 views

Test statistics in IR (t-test vs Wilcoxon vs signed test)

I have just read this paper about different test statistics one could use in Information Retrieval (IR), discussing whether Wilcoxon, Sign-test or Student t-test would be more reliable for comparing ...
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1answer
21 views

Missing data paired samples t-test

I have a list of insurance policies that filed claims in pre/post periods. I am trying to test whether the average cost of insurance claims per policy varied. Some of my policies don't have any claims ...
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0answers
16 views

How can I tease apart the role two variables play in an outcome?

I was wondering what type of statistical test I can use to find the role each variable plays in this scenario. We have an experiment set up with four groups (we are using drosophila flies). Group ...
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27 views

Unpaired t-test: large samples, unequal variances, unequal sample sizes

I a have two independent samples one with more than 700 observations and the second with more than 500 observations. I firstly use Cramér-von Mises test to test normality just to check how non-normal ...
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1answer
37 views

T-test or regression?

I have the following kind of data id age x 1 22 2.1 2 25 2.3 3 50 1.3 where $x$ is some measurement variable. I would like to show ...
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3answers
135 views

How to interpret negative 95% confidence interval?

I have performed an unpaired t-test on two groups of data: Group 1 (control): mean = 0.087 (n = 15) SD = 0.028 Group 2 (treatment): mean = 0.115 (n=12) SD = 0.042 The t-test ...
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0answers
17 views

In a two-way ANOVA, F-statistic for one factor is less than one and not significant. Much higher in t-test?

I conducted a two-way ANOVA (factors=season of birth and ethnicity) and found that the effect of ethnicity (Pakistani and White British) did not have a significant effect on child weight F(1, ...
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1answer
26 views

Mixed way ANOVA

I have two variables (group, achievement level). I want to check the effect of an intervention on different achievement levels. For example, I want to check whether there is an increase in achievement ...
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1answer
45 views

Method to determine the sample size for a one-sample t-test

What method is appropriate to use for determining a sample size for one sample t-test? How can I conduct the power analysis in this case? I am looking for the analytical formula that would allow me ...
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3answers
58 views

At what point do significantly different groups start to differ?

I have two groups: a control group (N = 91), and a treatment group (N = 54). I did a t-test in SPSS that suggests that there are significant differences between the two groups in terms of the variable ...
2
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1answer
21 views

Statistical test to perform on species diversity / Simpson's diversity index

I have a set of data from each of the two sites I am measuring for plant species diversity. I plan on using the Simpson's diversity index (SDI), which combines species richness (number of different ...
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35 views

Confused about whether to use t-tests or ANCOVA or ANOVA

I am investing whether vitamin C supplementation can attenuate creatine kinase increases after a strenuous workout. My participants are divided into two groups, VitC group and a Control (no ...
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0answers
14 views

Testing for significance between two average slopes

I have a question regarding my logic of how to go about checking for the significance between two average slopes. I hope my message comes across clear. The data I am analyzing consists of two sets, ...
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0answers
14 views

Wild bootstrap in “bordeline" case t-test

I have to compare the mean levels of a continuos variable y (ranging 1-20) subdividing my sample in two groups according to a dichotomous variables (i.e gender). Sample sizes of the two groups are ...
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38 views

Why to use randomized tests [duplicate]

I've learned that there are two types of tests: nonrandomized, where the test takes only two values $\psi:\mathcal{X}^n\to\{0,1\}$, and randomized where the test is $\psi:\mathcal{X}^n\to [0,1]$. In ...
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0answers
18 views

Repeated Measures ANOVA?

I am an undergraduate student studying psychology using SPSS to analyse my data. I have 2 conditions of the IV of treatment (treatment or no treatment) to test pain tolerance levels which is measured ...
0
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1answer
17 views

Can I conduct t-test for this study [duplicate]

In my study there are only 15 subjects in the intervention group and 15 in the control group. Can I use the relevant t-test to analyze each inter group and intra group differences(pre & post). ...
2
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2answers
29 views

Is it acceptable to use a paired t-test to compare my drug dosage data?

I have a table of patient demographics like height, weight, and some lab values, as well as data on the doses of a drug that the patients received. Using the patient demographic data, I also used a ...
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0answers
6 views

Sampling comparison groups based proportionality versus real-world frequency

I am looking at differential gene expression (using a t-test) in the context of five Breast Cancer Subtypes. I am working with data in which the distribution of subtypes matches real-world frequency ...
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26 views

Comparison of seasonal time series from different years

I'm analyzing air quality data from a 2-year sampling campaign in which we sampled concentrations of various air pollutants for 6 continuous weeks during each of: winter1, winter2. There was an ...
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0answers
8 views

Permutation test for 3 variates

I have 3 covariates, which are merely count data. They have 3 different means. How can I get a unique p-value or how can I compare them? The aim of my study is to know if those populations are ...
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20 views

Two-sample t-test (Welchs test) which distribution to sample from

I have the following problem: I have two weird distribution and I want to figure out which has the higher mean. To do that I can sample from either distribution and use a Welch's test to figure out ...
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0answers
21 views

correlation between spelling ability and frequency of use of text messaging

How can I correlate the frequency of time usage of text messaging with spelling ability? In our study we have 91 respondents given a spelling test with 25 items. We also ask respondents how long ...
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0answers
14 views

Gender differences against experimental IV conditions

I am a psychology student using SPSS to analyse my data. I have 2 conditions of the IV of treatment (treatment or no treatment) to test pain tolerance levels which is measured by the DV of pulse rate ...
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0answers
24 views

Shapiro-Wilk Output [duplicate]

I have data comprised into different variables (between females and males, measurements of body fat through 3 different methods) and after running a shapiro-wilk test, the output tells me parts of the ...
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0answers
18 views

Repeated Measures Design but also testing order effects in SPSS

I am a psychology student using SPSS to analyse my data. I have 2 conditions of the IV of treatment (treatment or no treatment) to test pain tolerance levels which is measured by the DV of pulse rate ...
0
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0answers
19 views

Which test would be appropriate to test multiple variables?

I have a data on users with 5 personality variables. The users had to pick a logo for three different projects (most likely, may be, least likely). The question is why the users chose the logo they ...
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0answers
29 views

Comparing paired data in two different treatment groups

Suppose I have two groups of participants. The first groups gets treatment 1 and the second group gets treatment 2. The first treatment is a standard treatment and the second treatment is something ...
1
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1answer
25 views

Regression Slope and a Bilateral Test

Well, I observe that the standard statistical software package tests regression coefficients if they are statiscally different from zero, that is, not specifically higher nor lower than zero -- a ...
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25 views

What does a p-value actually mean in a two-sample t-test? [duplicate]

Suppose I have two sets of samples, and I calculate a two-sample t-test, which gives me a two-tailed p-value of 0.0138. Is this the same as saying "The probability that the two sets are not ...
3
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2answers
76 views

Test two groups with only sample statistics or without distributional assumptions

I have two sets of samples, A and B. I want to find whether the underlying mean (i.e. if the sample size was infinite) of A is greater than that of B, to a certain confidence (95%). There are two ...
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6 views

paired subject design test of proportions

I am analyzing a performance data set and would like to compare across two different conditions. I have three subjects, which were tested over a number of trials. Each trial had a chance of being in ...
0
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0answers
23 views

About multiple testing and power analysis

Doing a power analysis for a single t-test is relatively simple. What if I have to do several tests? If I were to use the Bonferroni correction, I could just take the significance level as 0.05 ...
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1answer
23 views

Unequal sample size one way ANOVA

I want to compare the means of X between BMI groups, but have unequal sample sizes between my groups. ...
3
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1answer
60 views

What is not normal distribution?

I am running analyses for my dissertation and just got myself in a muddle. I am running descriptive stats to determine whether to use paired t-tests vs Wilcoxon signed rank tests. I've read that it ...
0
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0answers
14 views

Test if two means are significantly different in R [duplicate]

I would like to test if two means are significantly different from each other. I am using R and I do this: t.test(SampleA,SampleB) and I get output that looks ...
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0answers
44 views

Dissertation-results section

basically i am testing 2 species of pigs, 2 pigs of the same species in one enclosure and another 2 in a different enclosure, My aim is to see if alterations to feeding regimes have an effect on an ...
0
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1answer
20 views

Pre-post measurements with a control group

I am running a study looking at the effect of Vitamin C on muscle function. For my study design, I had 2 groups: A treatment (vit C) and a control (no treatment) group. Pre and post measurements were ...
0
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0answers
16 views

Performing t test, one-way ANOVA from mean and SD using SPSS

I have the following summarized data: Group 1: n=44, mean 12.1, SD 2.0 Group 2: n=56, mean 13.2, SD 2.5 Group 3: n=42, mean 12.7, SD 2.3 Is it possible to perform the t test comparing means of group ...
1
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1answer
45 views

Test if two gamma distributed populations are different

I have data from two populations of different sizes. Both have Gamma distributions with different shapes and scales (as estimated in r): fitdistr(x/10000, "gamma") #186 members shape 0.586219900 ...
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0answers
26 views

Comparing means between two groups if dependent variable is a percentage

I have data on recovery rates from several hospitals across the country. The recovery rates are in percentages. I want to compare the mean recovery rate between two groups of hospitals, one that uses ...
1
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1answer
35 views

Equivalent to Welch's t-test in GLS framework

How can Welch's t-test be expressed as a generalized least squares model? A standard independent samples t-test (where it is assumed that the samples being compared are drawn from populations with ...
2
votes
1answer
61 views

Size of Tukey's 1 Degree of Freedom Test

In Oehlert (p. 218) the following algorithm for computing Tukey's one degree of freedom test for non-additivity is suggested: Fit a preliminary model; this will usually be an additive model. ...
2
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1answer
64 views

simulate t-tests of mean differences

I would like to simulate t-tests of mean differences. I would like to simulate data based on 1) pre-specified (desired) mean difference between the variables and 2) desired t value 3) and p-value ...
2
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2answers
34 views

Should I use paired t-tests or ANOVA when comparing multiple variables from 2 tests?

I had 50 subjects perform two 30-minute cycling time trials on separate days. I would like to compare the means of several variables from each of the two tests: Cadence, Heart Rate, Power Output, and ...